The broad objectives of this research on the postmortem human lung are to correlate the elasticity of the lung with the microscopic structure of the fibroprotein networks of the interalveolar wall. This will be done by demonstrating and analyzing the intricate pattern of the collagen and elastin networks, through the use of automated light microscopy and digital imaging processing, and determining the alterations in the networks which occur with age and the lung volume changes of breathing. Random samples of the lung fixed by liquid fixative will be contrasted (compared) for residual lung integrity and fibroprotein patterns with lung quick-frozen, made anhydrous and fixed by osmium tetroxide. Elasticity of the lung will be determined by the pressure/volume response of air and liquid filled lung and the biaxial load test on isolated lung tissues. Special morphometric measurements involving alveolar size and collagen and elastin networks will provide the basis for connective tissue network analysis. The relationship between the network analysis and the various constitutive equations for the strain energy function of lung elasticity, the meaning of the material constants and their physical significance, the correlation between lung elasticity and fibroprotein network characteristics, the discussion of the air filled pressure volume curves and of the pressure volume curves of the liquid filled lung, the elastic properties derived from biaxial loading experiments, and the correlations among all these various parameters will give further understanding of lung elasticity.